How can I add icon to toolbar? Button doesn't work in v5

I’ve added several macros to the “tools” toolbar and they work properly. I did so originally when using LO 4, and was able to replace the text with an icon for each. Since going to LO 5.2, however, when I add a new macro the “modify icon” choice in the “customize” dialog seems to be working – but nothing changes on the toolbar. How can I replace the macro name with its icon?

Details: LO 5.3, Xubuntu 14.04.4

EDIT – Initially I used the details of a different machine. That one, with LO 5.1 and Xubuntu 16.04.1, works properly! It appears that something changed between 5.1 and 5.3.

This still puzzles me. I have LO installed on two machines; one has Xubuntu 14.04.5 on it and the other runs Xubuntu 16.04.2. On both, LO is at, from the “fresh” PPA. On the 14.04 box, the icon displays properly. On the 16.04 system, it does not.

However, other icons behave differently – only the top-left-hand portion of three custom icons appear on one, while on the other the same icons desplay properly, and in both cases these icons were imported from the same *.png files.

I found at least a partial solution to both of my problems not long after posting my comment. With the 16x16 images imported and assigned to the toolbar, I then went to the Options->View dialog and changed the setting for Toolbar Icons from “Automatic” to “small.” Success! both the no-icon-at-all situation and the partial-icon display vanished and all appears as I wanted it to be.

I’ve not tried going back to 26x26 images, or setting the option to “large” or “extra large” because I believe strongly in NOT fixing what ain’t broke – but I believe this result indicates that the problem lies somewhere in the automatic-scaling code for toolbar icons.

Hope this helps someone else!