"to" form?

[Nibble]

I've noticed in some manga I have that people occasionally take a word in "te" form, but replace the "te" with "to" -- for example, in Yotsuba& volume 1, the father says 「そこおいといていいぞ〜」 instead of 「そこおいていていいぞ〜」(which I translate as "You can leave it there"). Is there any reason for this? Is it common in spoken Japanese, or part of a certain dialect?

[Harisenbon]

It's a fairly common dialect. I know it from Gifu, but I'm sure that it's wider than that. Maybe the whole Kansai area?

They just replace て　with と in verbs.

ちょっと待っといて。など

[netarou]

「置いておいていいぞ。」→「置いといていいぞ。」
「さっさとしておけ。」→「さっさとしとけ。」
So, ておく becomes とく in conversation, I think.
In some region, ておく becomes ちょく though.
「そんなが捨てちょけ。」（土佐弁）＝「そんなの捨てとけ。」