Grendizer Saber

I sent an email to support. But since then I found something even weirder :
When I use <F4> instead of $F4, frame by frame playback doesn't behave the same. If I use <F4> and go to the next frame continuously, one frame every 2 frames is skipped!

Wow, what jlait said worked!
But yes, I think the file node is partly broken because it should accept the usual syntax $F4

Thanks but it doesn't work...
In File name, I tried :
D:/path/file.$F4.png
D:/path/file.F4.png
D:/path/file.<F>.png
D:/path/file.<F>4.png
Then I try to delay the sequence with video timing and it does nothing.

What's weird is that it does accept a syntax that's buggy on purpose, so I also tried :
D:/path/file.HAHA4.png
and each time I press "reload image" button and each time the frames are displayed.
My guess is : this parameter pane is buggy?