Please excuse us, but we are not sure what the bug is.
The <tbody> tag is mandatory for valid HTML and XHTML and is inserted automatically by the underlying browser engine. While it is possible to remove it using some client script, in general it is good practice to have it. In case you really need to remove the <tbody> tag from the HTML we will do our best to help you out, but please provide us with more information about your scenario.
As for the content that you insert - as you note yourself - this is plain wrong. HTML and XHTML rules do not allow for any tags or any content to be inserted between <table> and <tr> tag. Doing so greatly confuses both the browser editing engine and the editor. The editor is designed and aimed at handling HTML that abides to some basic rules.
We can log the problem and attempt to improve on it, yet we would appreciate more information on your scenario - why adding content at places where it is disallowed by rules is necessary?
Looking forward to hearing from you.
the Telerik team