This problem can be a bit annoying if you’re used to using the scheduled posts feature. But, like with any problem, there is solution, this time a quick and painless one.

Twitter Tools offers the possibility of setting up a default hashtag for your Tweets. Since this feature won’t work with the scheduled post, I took the liberty of seeing how this actually works – and to our luck – it uses custom fields. To be more precise, aktt_hash_meta custom field.
Therefore, when writing a scheduled post, simply add this custom field, and set it’s value to the hashtag you want to use, for example #ivanlistes. Save the post with this custom field added, schedule it, and that’s all there is to it.

It does require a bit more of work, but this way we don’t touch plugin’s original files, and we’re absolutely sure we won’t break something, cause future compatibility issues and so on.