In location /usr/share/pixmaps/pidgin/tray/Mint-X/status (from where my icon is loaded) are folders with icons in sizes: 16, 22, 32 and 48 pixels.
So I just added links: The problem with with scaling is, that it also scales the fonts without giving the user separate control over how much they're scaled.
I also have the issue (still running on Cinnamon 2.2.16) that sometimes the icon is actually rendered correctly, but I cannot right/left click to it (or rather said, nothing happens when I do). I think I found the easiest workaround of this issue.
My configuration: Linux Mint 17 64bit, Cinnamon 2.2.16, Pidgin 2.10.9 Pidgin launching at startup, "Allow Cinnamon to scale panel.." enabled Using 'looking glass' I have noticed, that there are 20x20px icons loaded.
The problem affects not only the Pidgin status icon, but also the Dropbox-Icon (Nautilus, not Nemo) and probably all other external status icons as well (I only have those two).
Switching to panel-edit-mode and moving the status-icon-applet around also lets the icons appear, but as soon as there is a change in the icons (blink on new message in pidgin or refreshing Dropbox) they disappear. Shame, i really hope this gets fixed soon, as it's pretty severe, and it affects some of the pre installed applications.
The changes in my test: I've just updated to Cinnamon 2.2.16 and this issue is still happening.
What I do is launch pidgin, wait for it to actually show up on the screen, then launch it again (won't run two copies) and then the indicator appears.
Has this been fixed in Linux Mint 17 Cinnamon (32-bit)? Just let me know if you need some hardware related infos maybe. Btw, a little workaround for those who closed Pidgin while it was minimized, and, when starting it again, the tray icon doesn't show up: Click the Pidgin launcher to bring up the contact list again, then, as described above, go into the preferences, and set tray icon visibility to "never show", and then "show always" again.
The Pidgin tray icon doesn't seem to disappear anymore on a status change. I fiddled in the Pidgin prefs, and set list_visible string to 1, because i didn't know clicking on the launcher makes the list visible again... Another workaround is to co to the pnael settings and change the panelsize a bit, then the icon appears and you can switch back to default size.