When I use an Extra Large Icon set (48x48 icons) as the default set, Opus also uses the icons for several dialogs,
but this doesn't look good, because there's not enough space for 48x48 icons.
I know I introduced these XL sets myself 
but it's probably easy to solve:
I think it's because that's the only icon size in the XL set, which is the default set. So Opus will look in there for those icons, and ones which are too large are the only choice it has.
You probably always want your default icon set to contain normal sized icons in addition to any other size that you want.
Leo, to test this I've now added the 32x32 set as 'small' icons to the 48x48 XL set, but this doesn't solve the problem with the dialogs: Opus still uses the XL version for the Dialogs.
And when I add the large icons as small icons there's also a new problem with the menu's (see screenshot below).
Of course one could only use the XL set as a second set and not as the default one, but wouldn't it be a better idea to make the Opus dialogs compatible with the 48x48 icons?
It would be a bit strange to add a warning to the XL sets: Please don't use this as your default set
Leo, I did some more tests and I think it's quite easy to solve this and to make the Opus Dialogs fully compatible with all iconsets/sizes:
<iconset name="DOpusIconTest">
<set filename="DOpusIconTest-small.png" height="22" size="small" width="22"></set>
<set filename="DOpusIconTest-large.png" height="32" size="large" width="32"></set>
</iconset>
TESTS:
Default ICONSET LARGE=32 + SMALL=22
Opus uses the LARGE ICONS OF THE FIRST (DEFAULT) iconset (32x32 icons) for the dialogs
Toolbars OK / Dialogs OK (with 32x32 icons)
Default ICONSET LARGE=32 (NO SMALL ICONS available)
Opus uses the LARGE ICONS OF THE FIRST (DEFAULT) iconset (32x32 icons) for the dialogs
Toolbars OK / Dialogs OK (with 32x32 icons)
Default ICONSET SMALL=22 (NO LARGE ICONS available)
Opus uses the LARGE ICONS OF THE SECOND iconset (32x32 icons) for the dialogs
Toolbars OK / Dialogs OK (with 32X32 icons)
Default ICONSET LARGE=22 (NO SMALL ICONS available)
Opus uses the LARGE ICONS OF THE FIRST (DEFAULT) iconset (22X22 icons) for the dialogs
Toolbars OK / Dialogs OK (with 22x22 icons)
Default ICONSET LARGE=48 (NO SMALL ICONS available)
Opus uses the LARGE ICONS OF THE FIRST (DEFAULT) iconset (48X48 icons) for the dialogs
Toolbars OK / Dialogs NOT OK (NOT ENOUGH SPACE FOR 48X48 ICONS)
Conclusion: Opus is looking for the SIZE attribute in the SET node of the first/default iconset for the Dialogs. When there is a large set available (SIZE='Large') in the first/default set, Opus uses this Large set for the Dialogs (even if the real size isn't 32x32). When Opus doesn't find a SIZE attribute with the value 'Large', Opus uses the icons of the second set with the value 'Large' for the Dialogs.
Solution: To make the Opus Dialogs fully compatible with all icon-sets/sizes Opus should look for the WIDTH and/or the HEIGHT attribute in the SET node of the first/default iconset and only use this set for the Dialogs if the width and/or height value is 32. When the first set doesn't contain icons with the size 32x32 Opus should look for 32x32 icons in the second set and use them for the dialogs.
