TYPO3 Core

Adding custom tags to RTE in TSConfig like this:
RTE.default {
proc {
allowTags := addToList(button,form)
allowTagsOutside := addToList(button,form)
denyTags := removeFromList(button,form)
entryHTMLparser_db {
allowTags < RTE.default.proc.allowTags
}
}
}
and this in Typoscript Setup:
lib.parseFunc_RTE.allowTags := addToList(button,form)

Adding the following code in the HTML source code, by clicking the "toggle text mode" button first and then adding the code:

<p>text</p><form action="index.php" method="post"><button>button</button></form>

After saving I got this:

<p>text</p><p></p><form action="index.php" method="post"><button>button</button></form><p></p>

How can I disable this automatically added p-tags?