Frame stepping GIFs is instant when going backwards, but laggy when going forwards

[MathiasSven]

Just as the title says, I am not sure what causes this behaviour. It is very obvious on some GIFs and less on others, but in any of them, if I just open them and then pause:

• Holding , after letting it play for a bit will smoothly step backwards
• Holding . will not do the same
• Pressing , is instantaneous
• Pressing . will have a slight delay (that delay being GIF dependent it seems)

Is there a way to get around this? Is this a bug or just an effect of some detail about how GIFs are implemented that I am not aware of? (Just like laggy step backwards on videos can be a product of the compression algorithms)